The present invention relates to worm driven servo actuated valves employing same of the type having a rotary valve member such as a blade, paddle or butterfly which is employed for directing flow of fluid or sonic pressure pulses in a passage such as the air inlet passage of an engine. Worm driven servo actuators are employed for numerous control purposes and arc particularly suitable for rotary valves. Valves of this type are employed as engine air throttles, communication, or diverter valves within the engine inlet manifold for directing flow or pulses to a desired passage during engine operation depending upon the conditions under which the engine is operating at the time. Heretofore, servo operated rotary valves for air flow control or communication in a passage, such as an engine inlet passage have utilized speed reducers or gear trains driven by a low voltage high RPM sub-fractional horsepower or low wattage motor. It has been found desirable to use such a small low wattage motor to reduce the cost and bulk of the motor drive particularly where the valve is to be mounted as a throttle actuator on the engine air inlet or through an aperture in the engine inlet manifold for use as a diverter valve.
Where a servo motor operated valve is employed for engine air throttle applications or as a manifold air diverter valve, it has been found difficult to provide adequate torque with a small low wattage motor to insure proper valve movement and to simultaneously provide the desired speed of response of the valve to changes in the electrical control signal to the motor. This has proven to be particularly troublesome for a servo operated motor for throttle actuation in conjunction with cruise control operation of the engine on a motor vehicle.
In providing a servo motor operated air flow valve for either an engine air throttle or inlet manifold diverter valve, it has been desired to use a worm and gear arrangement for speed reduction, torque multiplication and silence of operation. However, in the event of failure of the servo motor with the valve in an operating position it has been found extremely difficult to provide a spring return of the valve where a worm and gear drive arrangement has been employed.
Known techniques for providing a spring return of an engine air throttle valve having a worm and gear operated servo motor drive are shown and described in U.S. Pat. No. 5,950,765 issued in the name of J. E. Pearson, et al. wherein a worm and gear arrangement provides for engagement of a sector gear when a pinion coaxial with the worm has reached the end of a sector face gear with which the pinion is engaged. However, the system employed in the aforementioned Pearson, et al. patent has a multiplicity of gears, is complicated and the spring return is provided on the output sector gear and thus requires a relatively high spring rate to provide the return of the valve against the overall reduction ratio. The relatively high spring rate of the sector gear return spring results in increased power requirement for the drive motor and has rendered this arrangement not only relatively high in cost for mass production but also bulky and heavy for the engine air throttle applications.
Other known arrangements include the throttle servo actuator described in U.S. Pat. No. 5,138,211 to Haefner, et al. wherein a ball-detent actuated clutch is disengaged upon de-energization of the motor. In the aforesaid known servo motor operated valve employing a clutch, the clutch is described as unclutched by de-energization of a solenoid. However, this arrangement also is complicated and requires a multiplicity of parts, is difficult to assemble and is dependent upon proper release of the clutch solenoid to permit the spring to return the valve. In the aforesaid arrangement of Haefner, et al., motor failure without separate release of the clutch solenoid would not allow the return spring to return the throttle. Thus, it has been desired to find a low cost, simple and reliable way or means for operating an air flow valve with a servo motor utilizing a worm drive and to provide for spring return of the valve in the event of motor failure in any position without requiring a high torque motor and a multiplicity of gears.